The field of the invention is that of making photovoltaic cells, which enable light to be directly converted into electricity, deposited in thin films on a support by vacuum (CVD: “Chemical Vapour Deposition” and PVD: “Physical Vapour Deposition”) and “continuous” deposition methods.
The technology for making thin film photovoltaic cells, the interest of which has been shown over the last few years, concerns a type of cell (or module) obtained by depositing a thin film of semi-conductor on a support. The semi-conductor is thereby economised since it is not, as with crystalline silicon cells, sawn from a block. This technology should enable the production costs of photovoltaic cells to be significantly reduced in the future.
To use such a technology, different paths are possible:
Thin Film Crystalline Silicon
A thin film of polycrystalline silicon of 5 to 50 μm thickness is then deposited on a substrate. Such thin films should enable conversion yields of the same order as a cell on solid material to be obtained, given certain technological adaptations (optical confinement, texturing, etc.).
To carry out such a deposition, two techniques are currently possible: liquid phase epitaxy (LPE) growth, the main drawback of which is the use of a crystalline substrate and the following CVD techniques:                the pyrolytic decomposition of silane and hydrogen on a hot tungsten filament, which enables microcrystalline silicon (μc-Si) to be deposited on a glass substrate at 500° C. at relatively high rates (greater than 0.08 μm/min),        chemical vapour depositions (CVD) at temperatures above 800° C. in presence of a gas containing silicon (silane or chlorosilanes) and a doping gas (diborane or phosphine respectively for P— and N— doping), in which the presence of hazardous (silane) and toxic (phosphine) gases has a limitation in the long term in economic and environmental terms,        the most common techniques, which are CVD techniques and particularly the PECVD (“Plasma Enhanced Chemical Vapour Deposition”) technique, which enables silicon films to be deposited in a temperature range between 300° C. and 1200° C.        
But the yields obtained with such techniques remain below 10% and only reach values of 13-16% with a recrystallisation (thermal annealing) to increase the size of the grains. Better yields are expected for crystallites of large size (above 100 μm). However the supports must be able to withstand temperatures of around 800° C. in order to recrystallise the silicon: they are for example in ceramic.
Thin Film Amorphous Silicon
Amorphous silicon, despite its disordered structure, has an absorption coefficient greater than that of crystalline silicon. However, what it gains in absorption power, it loses in electrical charge mobility (low conversion yield), with a compromise nevertheless being viable. Making amorphous silicon photovoltaic cells requires less silicon and less energy than that of crystalline silicon cells.
But with this type of inexpensive material compared to other forms of silicon, low yields (7%) are obtained. Moreover, problems of stability quickly appear when said material is exposed to sunlight and weathering. Technological artifices such as the superposition of two p-i-n structures in “tandem” or three very thin active films, may be used to offset these disadvantages. The light degradation may then be reduced from 30% to 10%.
The simplest structure of an amorphous silicon cell comprises a boron doped zone, an intrinsic zone and a phosphorous doped zone (p-i-n structure). But the industrial yields obtained have stagnated for years under the 10% bar in terms of modules.
In addition, these technologies make use of complex architectures, which affect the production cost.
Thus, the technological limitations of devices of the prior art do not enable the following objectives to be obtained:                lifetimes greater than 20 years        production cost of around 0.5 Euros/Wc for a yield of 13%. (Wc or watt crest being the reference that corresponds to a nominal power delivered by a photovoltaic generator under optimal operating conditions).        
Indeed:                A deposition of silicon by PECVD cannot be carried out at sufficiently fast rates (typically between 0.01 and 0.1 μm/min).        The crystallisation of the silicon is generally achieved by thermal annealing. Technologies using an annealing by laser do not enable the depth of penetration of the laser energy to be controlled. The document referenced [1] at the end of the description describes the deposition of nanocrystalline silicon layers on graphite substrates by a PECVD method while heating the substrate. These layers are then recrystallised by means of a PEB (pulsed electron beam) crystallisation method. The presence of silicon crystals in the material before recrystallisation favours the crystallisation process. But the layers of nanocrystalline silicon have been elaborated by PECVD using hazardous and toxic gases such as trichlorosilane (SiHCl3) and hydrogen, contrary to sputtering and evaporation methods. Moreover, high temperatures (between 450 and 600° C.) are necessary to obtain these crystallised silicon films.        The optical trapping obtained by achieving an appropriate morphology of the support and the rear reflector is little developed. The texturing of the support is generally achieved by means of chemical baths, which are polluting methods characterised by slow speeds.        
The aim of the present invention is to resolve the abovementioned problems by proposing a method for making thin film photovoltaic cells (vacuum methods) based on silicon on a cheap, multifunctional support (flexible, unbreakable, excellent mechanical strength).